Cast iron of high magnetic permeability



5 2.5515 00- omom on ow on H. B. LAUDENSLAGER, JR., ETAL CAST IRON OF HIGH MAGNETIC PERMEABILITY Filed Jan. 29, 1963 June 15, 1965 9 8 mm N d. vww mL.. n r y w/y "E o .H H. u a s 2 United States Patent 3,139, 32 CAST RGN {11F HICH MAGNETEC PERlt ErsBiLiTY Harry B. Laudenslager, 3n, Jamestown, and Everett W.

Hale, Falconer, N.Y., assignors to Blackstone Corporation, a corporation of New York Filed .ian. 29, 1963, Ser. No. 254,730 6 Claims. (Cl. MES-35) 'lfis invention relates to cast iron having a high magnetic permeability and particularly to a composition of iron and a method of making such cast iron.

It is well known that cast irons have always been subject to severe limitations in the field where permeability is a desired or required factor. In general, the cast irons have been unsatisfactory for any use in which permeability was important and in such instances, one desiring permeability had to go to the steels in order to obtain this desired quality.

We have discovered a composition and a method of making a workable cast iron which has improved magnetic permeability properties approaching, if not equaling, those of steel. We have discovered that a cast iron falling within the following composition limits and treated as hereafter described will have high magnetic permeability. The composition of such an iron should fall within the following broad limits:

The balance iron with usual impurities in ordinary amounts. A preferred narrower range of composition is:

Percent Carbon 1.9 to Silicon 2.5 to Sulfur up to 0.008 Phosphorus up to Manganese up to Magnesium 0.025 to The balance iron with usual impurities in ordinary amounts.

The iron must be annealed so that the carbon is tempered and substantially completely free of combined carbon and flaked graphite after annealing. The melt is preferably agitated so as to react any oxygen in the system with silicon and magnesium and remove it as a part of the lag prior to castin It is important that the iron be substantially free from oxygen and oxides and that the sulfur and phosphorus be reduced to within the ranges above stated. This purging action may be accomplished by adding the magnesium into the molten metal with nitrogen gas so that the nitrogen agitates the bath as the magnesium enters it and promotes reaction with the oxygen of the bath. As this practice is carried out, it is important that there be added a sufficient amount of magnesium to provide the residual magnesium set out in the foregoing compositions.

This invention may perhaps best be understood by reference to the following example. A white cast iron composition was prepared with a base chemistry of 21% carbon, 1.5% silicon, 0.26% manganese, 0.045% sulfur and 0.045% phosphorus. This metal was tapped from the furnace at a temperature between 2880" F. and 2890 F. into a thousand pound ladle. Ten pounds of 85% calcium bearing ferrosilicon x 12 mesh was added to the metal in the ladle. Nitrogen was then injected into the ladle through a carbon tube (any other refractory tube such as ceramic might be substituted for the carbon tube) to agitate the metal and pure magnesium spheres were added to the nitrogen in the total amount of five pounds through the injection tube. The metal was then poured into castings without further treatment. The castings were annealed by a normal annealing cycle for malleable iron. The first stage graphitization was accomplished in about 8 hours at a temperature of 1690 F. The castings were then cooled to 1420 F. in about 2 hours and were then slow cooled from 1420" F. to 1260 F. at a rate at 10 per hour. As soon as the castings were cool enough to be handled, a ring was machined from the casting, wound and tested on a flux meter according to ASTM specification #341494B for flux testing of ferrous metal. Tests on these castings showed eight to ten kilolines higher than like castings made from Grade B malleable ASTM 32510, and from four to eight kilo-lines higher than Grade A malleable made to ASTM 35018 specifications.

Castings made from metal within the composition range ere disclosed and annealed by any good first-class heat treatment for malleable iron, such as that disclosed in the example, will produce high permeability approaching that for SAE 1006 steel. Comparative tests of conventional malleable iron, malleable iron of the present composition and treatment, and of SAE 1006 steel have been made. The test data is plotted in the figure which accompanies this application. It will be seen from a comparison of this test data that the cast iron of this invention has permeability properties far superior to that of ordinary malleable irons and comparable to magnetic types of steel.

In the figure, the several materials represented have the following compositions:

Curve Material 0 Si Mn S Mg Alloy of Invention 2. 14 2. 62 0. 28 0.008 0. 048

Conventional Grade B 2. 4-3 1 10 0. 40 0. 115 N o Malleable.

do 2. 50 1 20 0. 42 0.135 No SAE 1006 Steel Conventional Grade A 2.18 1. 52 0. 30 0. 063 N0 Malleable.

The material of this invention has proved satisfactory for use as a substitute for steel in the formation of a1- ternators for passenger cars, trucks and the like, a service for which no cast iron was acceptable prior to the present invention.

It is important that there be no cold working of the cast iron after the annealing cycle. If there is any cold working of the casting, it must be re-annealed so that all of the grain structure which has been altered by working is restored and carbon is converted to temper carbon during the heating treatment after casting.

While we have illustrated and described certain preferred practices and embodiments in the foregoing specification, it will be understood that this invention can be otherwise practiced within the scope of the following claims.

We claim:

1. A cast iron of high magnetic permeability comprising about 1.75% to 2.3% carbon, about 2% to 4% silicon, up to about 0.02% sulfur, up to about 0.05% phosphorus, up to about 0.4% manganese, about 0.025% to 0.05% magnesium and the balance iron with usual impurities in ordinary amounts, said iron having been cast white and having been annealed by a malleable iron heat treatment cycle to convert the carbon to temper carbon, said iron having a permeability of at least about kilolines/in. at 40 ampere turns per inch.

aaaaaoa 2. A cast iron of high magnetic permeabilitycompris ing about 1.9% to 2.15% carbon, about 2.5% to 3.5% silicon, up to about 0.008% sulfur, up to about 0.05% phosphorus, up to about 0.3% manganese, about 0.025 to 0.05 magnesium and'the balance iron with usual impurities in ordinalyamounts, said' iron'having been cast White and having been annealed by. a'rnalleable iro'n heat treatment cycle to convert the carbon to temper carbon, said iron having a permeability of at least about 80 kilolines/in. at 40 ampere turns per inch.

3. A cast iron of high magnetic permeability comprising about 1.75% to 2.3% carbon, about 2% to 4% silicon, up to .about'0.02% sulfur, up-to about 0.05% phosphorus,-up to about 0.4% manganese,'abouti0.025% magnesium, said iron being substantially fieeof oxygen and the balance iron with usual impurities in ordinary amounts,- said iron having been cast'white and having been annealed by a'malleable iron;heat-treatment cycle to convert the carbon to temper carbon, said'iron hav= ing apermeability of at'least about 80 kilo-lines/inPat 40 ampere turns per inch. 4; A' cast iron of high magnetic permeability comprisirrg about 1.9% to 2.15% carbon, about 2.5% to 3.5% silicon, up to about 0.008% sulfur, up to about 0.05% phosphorus, up to about 0.3% manganese, about 0.025% to 0.05% magnesium,saidiron'beingsubstantially free of oxygen and thebalance'iron with usual impurities in ordinary amounts, said iron having been cast white and amounts, adding to said mixture a suflicient amount of magnesium to provide a residual of about. 0.025% to 0.05 with an inert gas at a rate sufiicient to cause agitation of the molten metal mixture and to react silicon and magnesium with any oxygen present in the molten 'metal to remove substantially all theoxygen in the bath,

ten metal mixture comprising about 1.9% to 2.15% 'car-' bon, 2.5% ,to' 3.5% silicon, up to about 0.008% sulfur, up to about 0.04% phosphorus, up to about 0.3% manganese and the balance iron with usual impurities in ordinary amounts,adding to said mixture a sufiicient amount of magnesium-to provide a residual of about 0.025% to 0.05 with an inert gas at a rate suflicient toc'ause agihaving beenannealed by a malleable iron heat treatment cycle to convert the carbon to' temper carbon; said iron having a permeability of'at least about 80 kilo-lines/in.

tation of the molten metal mixture and to react silicon and magnesium with any oxygen, sulfur and phosphorus in the mixture to remove substantially all of the oxygen from the bath and reduce the level of phosphorus and sulfur below the maximum herein claimed, cooling said mixture and annealing to convert the carbon to temper carbon, said iron having a permeability of at leastiabout 80 kilo-lines/in'. at 40 ampere turns per, inch.

References Cited by the Examiner UNITED STATES PATENTS 2,578,794 12/51 Gagnebin et a1. +123 FOREIGN PATENTS 9/52 Great'Britain'. 

1. A CAST IRON OF HIGH MAGNETIC PERMEABILITY COMPRISING ABOUT 1.75% TO 2.3% CARBON, ABOUT 2% TO 4% SILICON, UP TO ABOUT 0.02% SULFUR, UP TO ABOUT 0.05% PHOSPHORUS, UP TO ABOUT 0.4% MANGANESE, ABOUT 0.025% TO 0.05% MAGNESIUM AND THE BALANCE IRON WITH USUAL IMPURITIES IN ORDINARY AMOUNTS, SAID IRON HAVING BEEN CAST WHITE AND HAVING BEEN ANNEALED BY A MALLEABLE IRON HEAT TREATMENT CYCLE TO CONVER THE CARBON TO TEMPER CARBON, SAID IRON HAVING A PERMEABILITY OF AT LEAST ABOUT 80 KILOLINES/IN.2 AT 40 AMPERE TURNS PER INCH. 